The impact of Zn2+ doping in modifying the surface, structural, and photocatalytic properties of β-Ca3(PO4)2

Abstract

In this study, the impact of Zn²⁺ doping on β-Ca₃(PO₄)₂ characteristics was investigated with particular focus on its influence on the surface, structure, and photocatalytic properties. Zn²⁺ doped β-Ca₃(PO₄)₂ (Zn_x-TCPs) were synthesized using a solid-state method and were thoroughly studied to evaluate the modification induced by cationic substitution. The structural analysis revealed a noticeable shrinkage in the lattice parameters a and c and the unit cell volume induced by Zn²⁺ doping. Minor spectral changes in the vibrational modes of PO₄^3- were also observed in the infrared and Raman spectra of Zn_x-TCPs. The influence of doping on the materials' morphology was insignificant; however, molten grain boundaries were noticeable at high Zn concentration, x ≥ 1. X-ray photoelectron spectroscopy (XPS) revealed that the surface of the doped materials was rich in Zn. Optical absorption measurements indicated that Zn²⁺ doping slightly affects the optical bandgap of β-Ca₃(PO₄)₂. The photocatalytic activities of the materials were investigated for the degradation of Rhodamine B (RB) and Methylene blue (MB). The photocatalytic experiments were carried out in the presence of hydrogen peroxide and under simulated solar light. The samples exhibited enhanced catalytic activity compared to β-Ca₃(PO₄)₂, and the Zn_0.5-TCP sample demonstrated the highest degradation efficiency. This sample showed excellent stability during the reusability tests, which suggests the suitability of Zn_0.5-TCP for use as an efficient photocatalyst. Surface defects are believed to play an important role in the production of active species during the photocatalytic reaction.

Keywords: Dye degradation; Photocatalytic activity; Structural properties; Surface defects; Zn(2+) doped β-TCP.